1. Field of the Invention
This invention relates to a roller contact device suitable for use in a tap changer or the like, and more particularly to improvement in a roller contact device having a couple of roller contacts in parallel.
2. Description of the Prior Art
Illustrated in a sectional view in FIG. 1 is a conventional roller contact device as disclosed in Japanese Utility Model Publication No. 52-25638, in which indicated at lA and lB are a pair of stationary contacts and at 2 is a roller contact which is to be bridged to connect the two stationary contacts and rotatably fitted on a roller shaft 3. Denoted at 4A and 4B are a pair of support shafts which are supported in bores 5a and 5b for movements toward and away from the stationary contacts lA and lB, respectively. The support shafts 4A and 4B are provided with bores 4c and 4d respectively in the fore end portions to support the opposite ends 3a and 3b of the roller shaft 3 tiltably and rotatably therein. Indicated at 6 are stop rings which are fitted on rear end portions of the support shafts 4A and 4B, and at 7A and 7B are compression springs which are provided in the bores 5a for urging the support shafts 4A and 4B toward the stationary contacts lA and lB, respectively.
The above-described conventional device operates in the manner as follows.
In the contact closing position, the support shafts 4A and 4B are constantly pushed forward by the compression springs 7A and 7B due to the existence of a gap space between the drive arm 5 and each stop ring 6. Consequently, the roller contact 2 is pressed against the stationary contacts lA and lB through the roller shaft 3.
The roller shaft 3 is tiltably supported on the support shafts 4A and 4B, so that, in case there is a difference in height between the contacting surfaces of the stationary contacts lA and lB, the roller contact 2 is tilted to contact invariably both of the stationary contacts lA and 1B.
As the drive arm 5 is turned (in a direction perpendicular to the face of the drawing) by a contact opening operation, the roller contact 2 is disengaged from the stationary contacts lA and lB, and the support shafts 4A and 4B are each moved forward into a position where the stop ring 6 is abutted against the drive arm 5.
Although a single roller contact 2 is shown in the above-described conventional device, a pair of roller contacts are mounted in parallel as shown in FIG. 2 in a case involving an increased current capacity, using two sets of paired support shafts 4A and 4B and two sets of the compression springs 7A and 7B of FIG. 1.
The conventional roller contact device having a pair of roller contacts arranged in such a manner has problems or drawbacks that it requires an increased number of component parts as a result of the provision of two sets of support shafts 4A and 4B and two sets of compression springs 7A and 7B, which cause a number of steps in the machining process for forming bores in the drive arms to redouble and accordingly the assembling time to increase.